using System.Collections.Generic;
using System.Linq;
using NUnit.Framework;
using ProjectEuler.Core.Helpers;

namespace ProjectEuler.Core
{
    public class Problem8 : IProjectEulerProblem
    {
        private readonly string digits =
            @"73167176531330624919225119674426574742355349194934
            96983520312774506326239578318016984801869478851843
            85861560789112949495459501737958331952853208805511
            12540698747158523863050715693290963295227443043557
            66896648950445244523161731856403098711121722383113
            62229893423380308135336276614282806444486645238749
            30358907296290491560440772390713810515859307960866
            70172427121883998797908792274921901699720888093776
            65727333001053367881220235421809751254540594752243
            52584907711670556013604839586446706324415722155397
            53697817977846174064955149290862569321978468622482
            83972241375657056057490261407972968652414535100474
            82166370484403199890008895243450658541227588666881
            16427171479924442928230863465674813919123162824586
            17866458359124566529476545682848912883142607690042
            24219022671055626321111109370544217506941658960408
            07198403850962455444362981230987879927244284909188
            84580156166097919133875499200524063689912560717606
            05886116467109405077541002256983155200055935729725
            71636269561882670428252483600823257530420752963450";

        private string ThousandDigits
        {
            get
            {
                return digits.RemoveWhitespace();
            }
        }

        public IList<int> AllProductsOfNConsecutiveNumbers(string nums, int n)
        {
            if(string.IsNullOrEmpty(nums) || n > nums.Length)
            {
                return new List<int>();
            }

            var productList = new List<int>();

            int endIndex = nums.Length - n;
            
            for(int i=0; i<=endIndex; i++)
            {
                var product = 1;
                for(int j=0;j<n;j++)
                {
                    product *= int.Parse(nums[i + j].ToString());
                }
                productList.Add(product);
            }

            return productList;
        }

        public int Number
        {
            get { return 8; }
        }

        public string Description
        {
            get { return "Find the greatest product of five consecutive digits in the (given) 1000-digit number"; }
        }

        public string Answer
        {
            get { return AllProductsOfNConsecutiveNumbers(ThousandDigits, 5).Max().ToString(); }
        }
    }

    [TestFixture]
    public class Problem8_tests
    {
        [Test]
        public void GreatestProductOfNConsecutiveNumbers_should_work_for_simple_cases()
        {
            var p = new Problem8();

            Assert.AreEqual(0, p.AllProductsOfNConsecutiveNumbers("",1).Count);
            Assert.AreEqual(9, p.AllProductsOfNConsecutiveNumbers("9", 1).Max());
            Assert.AreEqual(9, p.AllProductsOfNConsecutiveNumbers("99", 1).Max());
            Assert.AreEqual(81, p.AllProductsOfNConsecutiveNumbers("99", 2).Max());
            Assert.AreEqual(81, p.AllProductsOfNConsecutiveNumbers("218149982098", 2).Max());
            Assert.AreEqual(9*9*9*9*9, p.AllProductsOfNConsecutiveNumbers("218149999982098", 5).Max());
        }
    }
}